1. Field of the Invention
The present invention relates to a gateway, and more particularly to a gateway for supporting communications between network devices connected to different networks.
2. Description of the Related Art
With a recent development of communication technology, high-speed data service networks are widespread. Against this backdrop, more and more companies developing and manufacturing digital information home appliances having networking functions, such as refrigerators, digital TVs and set-top boxes which are connectible to the Internet. As these home appliances are enabled to operate as information terminals with network functions added thereto, a new form of network, that is, a home network has been developed.
Electric/electronic products forming a home network at home may be connected to the Internet in a wire or wireless manner, so that a user can transmit and receive information and control electric/electronic products through the Internet, regardless of the user's location, such as homes, remote places and so on.
In order to connect electric/electronic products to the Internet, new types of network devices are provided in homes with necessary programs embedded. Among the network devices, a home gateway operates to connect the home network with the Internet and control the flow of the network packets.
Currently, each home is given one public Internet Protocol (IP) address from an Internet Service Provider (ISP) to connect to the Internet by using a basic home gateway such as an Asymmetrical Digital Subscriber Line (ADSL) and a Cable modem.
These conventional home gateways provide a simple connecting service which connects one home network to the Internet. Meanwhile, a recent trend requires a variety of services to be provided through a home gateway because a plurality of network devices can be used in homes, small office home business (SOHO) and in-house work are widespread, and appliances automation and remote controls are being actively developed. However, the conventional home gateways do not satisfy the current demands.
In order to meet the demands of the customers, a method using private IP addresses has been proposed for a home network. This method applies the network address port translation (NAPT) technology to a home gateway in order for a plurality of network devices of a home network to access the Internet with one shared IP address.
The problem is that an IP address of a home gateway frequently changes, thus requiring a user to find out the current IP address every time the user wants to hook up to the home network connected to the Internet. In order to solve this problem, a technology has been proposed in which a home gateway is given an IP address from an ISP and then a domain name of the home gateway and the assigned IP address are registered in a dynamic Domain Name Server (DNS) server on the Internet. According to this, the user can get access to appliances at his or her home through the domain name rather than the IP address.
A home gateway is given one IP address from an ISP, but, since a plurality of information devices are used at home in a home network environment, there exists a problem that the devices can not be simultaneously connected to the Internet with the shared IP address. Accordingly, private IP addresses are used at home, and the NAPT technology is used that connects information devices to the Internet by using one shared IP address.
If there are packets outgoing to the Internet from a home, the NAPT translates a private IP address of packet source and a source port number into an assigned IP address and a different port number which are recorded in an NAPT translation table. If response packets to the above are forwarded to a home network from the Internet, the home gateway refers to the NAPT table, translates an IP address of packet destination and a destination port number into a private IP address and a port number, and forwards the response packets to the final destination. Packets are abandoned if the packets forwarded to a home network from the Internet are not recorded in the NAPT table.
The use of the NAPT technology enables access to the Internet from a home network. That is, a plurality of network devices on a private network can get access to the Internet by sharing one IP address. However, it is impossible for the network devices to get access to a home network from the Internet because information is not known in advance such as a private IP address and port, home gateway port number, IP address and port, and IP protocol, that are recorded in the NAPT table in order for packets sent by an outside user hooking up to the Internet to be translated and routed through a home gateway into a private network.
A Virtual Private Network (VPN) is a technology applied to a home gateway in order for a user hooking up to the Internet to be able to get access to network devices from outside. VPNs may vary depending upon environments and network hierarchies applied, but, in the home network environments, 2-layer tunneling protocols such as Point-to-Point Tunneling Protocol (PPTP) and Layer Two Tunneling Protocol (L2TP) are widely used. Each home gateway has a VPN server, and a remote user connected to the Internet operates as a VPN client. The home gateway of each home network can operate as a VPN server or a VPN client in each home network. First, a VPN client requests a VPN server to set up a tunnel by using an IP address on the Internet. If the tunnel is set up, the VPN server authenticates the VPN client, and allocates to the VPN client a private IP address that the client can use inside the home network. The VPN client creates a virtual network interface by using the allocated private IP address, and the interface is connected to the home network and operates like one network. The IP address of the VPN client is used to set up a tunnel to the VPN server, and the private IP address is used in the home network connected through the tunnel.
As described above, the application of the NAPT and VPN technologies to the home gateway enables connections to the Internet through a plurality of network devices at home, and remote users on the Internet to connect to the home network.
However, the above technologies such as NAPT and VPN connect home networks with the Internet, but have a problem that they can not provide connections between an arbitrary home network and another home network. Because a home network uses private IP addresses, a plurality of home networks using different IP addresses may use identical private IP addresses at the same time. If a host connected to a home network transfers data and the host belonging to the home network has the identical IP address as a host belonging to a remote home network, errors occur upon data transmissions since a decision can not be made on a device belonging to which home network the data is transmitted to.